Postnatal development of sound pressure transformations by the head and pinnae of the cat: Monaural characteristics

Abstract

Although there have been many anatomical, physiological, and psychophysical studies of auditory development in cat, there have been no comparable studies of the development of the sound pressured transformations by the cat head and pinnae. Because the physical dimensions of the head and pinnae determine the spectral and temporal transformations of sound, as head and pinnae size increase during development, the magnitude and frequency ranges of these transformations are hypothesized to systematically change. This hypothesis was tested by measuring directional transfer functions ͑DTFs͒, the directional components of head-related transfer functions, and the linear dimensions of the head and pinnae in cats from the onset of hearing ͑ϳ1.5 weeks͒ through adulthood. Head and pinnae dimensions increased by factors of ϳ2 and ϳ2.5, respectively, reaching adult values by ϳ23 and ϳ16 weeks, respectively. The development of the spectral notch cues to source location, the spatial-and frequency-dependent distributions of DTF amplitude gain ͑acoustic directionality͒, maximum gain, and the acoustic axis, and the resonance frequency and associated gain of the ear canal and concha were systematically related to the dimensions of the head and pinnae. These monaural acoustical properties of the head and pinnae in the cat are mature by 16 weeks.

Concurrent Development of the Head and Pinnae and the Acoustical Cues to Sound Location in a Precocious Species, the Chinchilla (Chinchilla lanigera)

“…We tested the hypothesis that the increases in acoustic directionality during development were determined by increasing pinnae dimensions by modeling the pinnae as a circular aperture (Calford and Pettigrew 1984;Coles and Guppy 1986) and then comparing the outputs of this model to the empirical acoustical measurements. Our results fit well with previous studies showing that the frequency dependence of diffraction of sound into a circular aperture accounts qualitatively for the area of acoustic directionality (Calford and Pettigrew 1984;Coles and Guppy 1986;Carlile and Pettigrew 1987;Musicant et al 1990;Obrist and Wenstrup 1998;Tollin and Koka 2009b). Our data demonstrate that the increasing dimensions of the pinnae during development were accompanied by increased acoustical directionality.…”

“…4E). This trend is consistent with the hypothesis that an increased-size pinna will interact with sounds of progressively lower frequencies (see Tollin and Koka 2009b). FNFs fall fully into the adult range by~P45, corresponding to when the pinna dimensions become mature.…”

“…We hypothesized that for a given frequency, the solid area enclosed by the −3-dB contour should decrease with the age of the animal because the linear dimensions of the external ear increase during development. To test this hypothesis, the equation describing the frequency dependence of the solid angle for a −3-dB contour for acoustic diffraction through a circular aperture for a given aperture diameter (equation derived in Calford and Pettigrew (1984), and Coles and Guppy (1986); see also Tollin and Koka (2009b)) was fitted to the acoustical data for nine animals (only those animals for which we measured DTFs at the full 525 locations were used here) at different ages ranging from P0-1 to adult. In fitting the aperture, diameter was the only free parameter (MATLAB® Version 7.1 robust nonlinear least squares trust-region method).…”

Using Virtual Acoustic Space to Investigate Sound Localisation

“…The lower border for ILD extraction, likewise, seems to be related to the observation that the head of an animal only creates sufficiently large ILDs above a certain frequency. These conclusions are supported by data from animals such as the cat, the ferret, monkey and the barn owl (Koeppl, 1997;Koka et al, 2008;Moiseff and Konishi 1981;Parsons et al, 2009;Spezio et al, 2000;Tollin & Koka, 2009). The use of both ITDs and ILDs in azimuthal sound localisation is known as duplex theory (Blauert, 1997;Macpherson & Middlebrooks, 2002;Rayleigh, 1907).…”

Influence of Sound Source Location on the Behavior and Physiology of the Precedence Effect in Cats

“…In addition to creating acoustical cues such as the interaural level difference, the average binaural sound level (i.e., the arithmetic average of the SPL at the two ears) changes as well. There are no published reports in the literature of ABL for adult cats, so we computed it from the data in Tollin and Koka (2009). For frequencies from 1-25 kHz and azimuths between Ϯ50°about the midline, the ABL in adult cats decreases as a source is moved laterally away from the midline (ABL is 0 dB at the midline), but by Ͻ5 dB.…”